This invention relates to improvements in a cylinder block, more particularly to a structure of oil dropping passage formed in the cylinder block.
In an automotive internal combustion engine, a cylinder head is usually fastened to a cylinder block by screwing bolts into boss sections of the cylinder block in which each boss section is formed in a cylinder block side wall and located between adjacent cylinders. Additionally, oil dropping passages are formed in the cylinder block side wall to introduce lubricating oil to be returned to an oil pan. In case that the oil dropping passage is intended to be formed in the boss section formed with a bolt hole into which the bolt is screwed, it is necessary to form the boss section large. In this regard, it is general to form the oil dropping passage at a position separate from the boss section.
Additionally, Japanese Patent Provisional Publication No. 2000-213411 discloses a cylinder block formed with an oil dropping passage which has an upper end opened to an upper deck and a lower end opened to the upper side section of a crank chamber. The cross-sectional area of the oil dropping passage is varied in an axial direction of the passage. In other words, the lower section of the oil dropping passage is enlarged in cross-sectional area as compared with the upper section of the passage.